The present invention relates to a nuclear fuel assembly including a fuel bundle and a tie plate for supporting the fuel assembly and, particularly, relates to a debris shield attached to the Upper Tie Plate (UTP) of the fuel bundle assembly.
In a fuel assembly, liquid coolant/moderator flows into the assembly thru the bottom and exits as a water/steam mixture from the top. The core includes a plurality of fuel bundles arranged in vertical side-by-side relation, each containing a plurality of fuel rods. The fuel bundles include a housing formed by a hollow metal channel. The fuel bundles also include one or more tie plates that support the fuel rods in the bundle. Generally a bundle includes an upper tie plate near the top of the fuel assembly and a lower tie plate at the bottom of the fuel assembly.
Debris may fall through a conventional upper tie-plate and become lodged within the fuel assembly where the debris may cause fuel rod fretting during normal operating conditions. Fretting is potentially damaging to the fuel rods, resulting in what is typically known as a “leaker”.
Conventional efforts to address debris falling down into a fuel assembly typically focus on prevention of debris within the coolant itself and coolant flow passages. Conventional efforts typically involve administrative controls regarding the treatment of coolant flow passages and handling of fuel assemblies such that debris does not enter the passages or the fuel assemblies. These controls are designed to alleviate the sources of debris such that debris does not fall down into fuel assemblies. Nevertheless, there is a risk that debris will fall into a fuel assembly, especially while the coolant flow stops and the reactor core is open. There is a long felt need for procedures and devices to ensure that debris does not fall into fuel assemblies, especially while the coolant flow is stopped, during refuel operations, and in a reverse coolant flow pattern.